Electronic device

ABSTRACT

To provide an electronic device capable of bright image display. A pixel is structured such that a switching TFT and a current controlling TFT are formed on a substrate and an EL element is electrically connected to the current controlling TFT. A gate capacitor formed between a gate electrode of the current controlling TFT and an LDD region thereof holds a voltage applied to the gate electrode, and hence a capacitor (condenser) is not particularly necessary in the pixel, thereby making the effective light emission area of the pixel large.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electronic device having an elementthat is comprised of a light emitting material sandwiched betweenelectrodes, and to an electric apparatus using the electronic device forits display unit (display or display monitor). Specifically, the presentinvention relates to an electronic device using a light emittingmaterial that provides EL (Electro Luminescence) (Note that the materialwill hereinafter be called EL material).

2. Description of the Related Art

In recent years, development is proceeding in an electronic device usinga self light emitting element that utilizes the EL phenomenon of a lightemitting material (hereinafter referred to as EL element) (the devicewill hereafter be referred to as EL display device). The EL displaydevice is a display device that uses a self light emitting element and,hence, unlike a liquid crystal display device, does not need abacklight. In addition, the EL display device has a wide angle of view,which makes the device a promising candidate for a display unit of aportable apparatus for outdoor use.

There are two kinds of EL display device: a passive type (passive matrixtype) and an active type (active matrix type), and both types are beingdeveloped actively. However, what draws attention most is, at present,an active matrix type EL display device. The EL material emitting EL andforming a light-emitting layer also is divided into two types, one beingan organic EL material and the other being an inorganic EL material. Theorganic material is further divided into a low molecular weight type(monomer type) organic EL material and a high molecular weight type(polymer type) organic EL material. The polymer type organic EL materialparticularly highly regarded, or it is easier to handle and has higherheat resistance in comparison with the low molecular weight type organicEL material. Incidentally, a light-emitting device using an organic ELmaterial is called OLED (organic light emitting diode) in Europe.

The active matrix type EL display device is characterized in that eachof pixels that constitute a pixel portion is provided with an electricfield transistor, recently, a thin film transistor (hereinafter referredto as TFT), to control the amount of current flowing through an ELelement by the TFT. As a typical pixel structure for such an activematrix type EL display device, there is known a structure illustrated inFIG. 1 attached to Japanese Patent Application Laid-open No. Hei8-241048.

The pixel structure disclosed in the publication sets two transistors(T1, T2) in one pixel, and a capacitor (condenser: Cs) is provided in adrain of the transistor (T1) parallel to the transistor (T2). Thiscapacitor (condenser) is necessary for holding a voltage applied to agate of the transistor (T2) for one field period or one frame period.

When two transistors and a capacitor (condenser) are formed in one pixelhowever, these elements occupy almost all the pixel area, causing areduction of the effective light emission area (the area in which lightemitted from a light-emitting layer is allowed to transmit to be used).

SUMMARY OF THE INVENTION

The present invention has been made in view of the above problem, and anobject of the present invention is therefore to provide an electronicdevice capable of bright image display by using a pixel structure with alarge effective light emission area. Another object of the presentinvention is to provide an electronic device of high reliability. Stillanother object of the present invention is to provide an electricappliance using the electronic device as its display unit.

Yet still another object of the present invention is to provide aprocess for reducing the cost of manufacturing the electronic devicecapable of displaying an image with high brightness.

The present invention is characterized in that a voltage applied to agate of a TFT for supplying current to an EL element (hereinafterreferred to as current controlling TFT) is held by a gate capacitor(parasitic capacitor formed between the gate and an active layer) of thecurrent controlling TFT. In other words, the present invention activelyutilizes the gate capacitor of the current controlling TFT(corresponding to the transistor (T2) in FIG. 1 of Japanese PatentApplication Laid-open No. Hei 8-241048) instead of the capacitor(condenser: Cs) shown in FIG. 1 of Japanese Patent Application Laid-openNo. Hei 8-241048.

The present invention is characterized in that an LDD region is formedon a drain region side of the current controlling TFT that is comprisedof a P-channel TFT so that the LDD region overlaps with a gate electrodethrough a gate insulating film sandwiched therebetween. Usually, aP-channel TFT is used without forming therein any LDD region, and thusthe invention is characterized by forming the LDD region in order toform the gate capacitor.

The structure as such practically dispenses with the area the capacitor(condenser) occupies, thereby greatly increasing the effective lightemission area.

The EL display devices referred to in this specification includetriplet-based light emission devices and/or singlet-based light emissiondevices.

The present invention employs a process of manufacturing a plurality ofelectronic devices from one large-sized substrate in order to reducemanufacturing cost of the electronic device, namely, to produce a lowcost electronic device. The characteristic of the present inventionresides in considerably reducing the manufacturing cost by limiting theinvestment in plant and equipment to a minimum with employment of aprocess to which an existing production line for liquid crystal can beapplied.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the cross sectional structure of the pixelportion of an electronic device of the present invention;

FIGS. 2A and 2B are diagrams showing the top structure and theconfiguration, respectively, of the pixel portion of the presentinvention;

FIGS. 3A to 3E are diagrams showing manufacturing processes of an activematrix substrate of Embodiment 1 ;

FIGS. 4A to 4D are diagrams showing manufacturing processes of theactive matrix substrate of Embodiment 1 ;

FIGS. 5A to 5C are diagrams showing manufacturing processes of theactive matrix type substrate of Embodiment 1 ;

FIG. 6 is an enlarged diagram of the pixel portion of the presentinvention;

FIG. 7 is a diagram showing the circuit block structure of an EL displaydevice of Embodiment 1 ;

FIGS. 8A and 8B are cross sectional diagrams of an EL display device ofEmbodiment 1;

FIGS. 9A to 9C are diagrams showing the circuit structures of an ELdisplay device of Embodiment 2;

FIGS. 10A and 10D are cross sectional diagrams of the current controlTFTs of Embodiment 3;

FIGS. 11A and 11B are diagrams showing processes of obtaining multiplenumber of an EL display device of Embodiment 4;

FIGS. 12A and 12B are diagrams showing the processes of obtainingmultiple number of an EL display device of Embodiment 4;

FIGS. 13A and 13B are diagrams showing the processes of obtainingmultiple number of an EL display device of Embodiment 4;

FIGS. 14A to 14F are diagrams showing specific exams of electricapparatus of Embodiment 9;

FIGS. 15A and 15B are diagrams showing specific examples of electricapparatus of Embodiment 9; and

FIGS. 16A and 16B are photographs showing images of the EL displaydevice of Embodiment 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[Embodiment Mode]

An embodiment mode of the present invention will be described withreference to FIG. 1 and FIGS. 2A and 2B. Shown in FIG. 1 is a sectionalview of a pixel portion of an EL display device according to the presentinvention, and FIG. 2A is a top view thereof whereas FIG. 2B illustratesthe circuit structure thereof. Actually, plural pixels are arranged in amatrix-like manner to form the pixel portion (image display portion).Common reference symbols are used in FIG. 1 and FIGS. 2A and 2B.Therefore, the drawings can be cross-referred. Two pixels shown in thetop view of FIG. 2A share the same structure.

In FIG. 1, reference symbol 11 denotes a substrate and 12 denotes aninsulating film that serves as a base (hereinafter referred to as a basefilm). Substrates usable as the substrate 11 include a glass substrate,a glass ceramic substrate, a quartz substrate, a silicon substrate, aceramic substrate, a metal substrate, and a plastic substrate (includinga plastic film).

The base film 12 is effective particularly when using a substratecontaining a movable ion or a substrate having a conductivity. However,the base film is not necessarily provided on a quartz substrate. Aninsulating film containing silicon is suitable for the base film 12. Theterm “an insulating film containing silicon” herein designates,specifically, an insulating film containing, in given proportions,silicon, and oxygen or nitrogen, such as a silicon oxide film, a siliconnitride film, or a silicon oxide nitride film (expressed as SiOxNy).

To give heat releasing action to the base film 12 to release heatgenerated from the TFT is also effective in preventing degradation ofthe TFT or degradation of the EL element. Any known material may be usedto impart to the base film the heat releasing action.

In FIGS. 2A and 2B, two TFTs are formed in each pixel. Reference symbol201 denotes a TFT functioning as a switching element (hereinafterreferred to as a switching TFT) and 202 denotes a TFT functioning as acurrent controlling element (hereinafter referred to as currentcontrolling TFT) for controlling the amount of current flowing into theEL element. The switching TFT 201 is composed of an N-channel type TFTwhereas the current controlling TFT 202 is composed of a P-channel TFT.

However, according to the present invention, the switching TFT and thecurrent controlling TFT are not necessarily limited to the abovecombination of N-channel TFT and P-channel TFT. The switching TFT 201may be formed from a P-channel TFT, or both the switching TFT and thecurrent controlling TFT may be formed from N-channel TFTs.

The switching TFT 201 is formed to have a source region 13, a drainregion 14, LDD regions 15 a to 15 d, an active layer including a highconcentration impurity region 16 and channel forming regions 17 a, 17 b,a gate insulating film 18, gate electrodes 19 a, 19 b, a firstinterlayer insulating film 20, a source wiring 21, and a drain wiring22.

As shown in FIG. 2A, the gate electrodes 19 a, 19 b constitute thedouble gate structure in which a gate wiring 211 formed from a materialdifferent from a material used for forming the gate electrodes 19 a, 19b (the former material is less resistive than the latter material)electrically connects the gate electrode 19 a to the gate electrode 19b. The structure of the gate electrodes of course is not limited to thedouble gate structure, but may be a multi-gate structure (a structure inwhich a plurality of TFTs are connected in series) such as the triplegate structure.

The multi-gate structure is very effective in lowering an OFF currentvalue, and, in the present invention, the switching TFT 201 of the pixeltakes the multi-gate structure to thereby form a switching elementhaving a low OFF current value. The LDD regions 15 a to 15 d in theswitching TFT 201 are formed so as not to overlap with the gateelectrodes 19 a, 19 b through the gate insulating film 18 sandwichedtherebetween. This structure is very effective in lowering the OFFcurrent value.

It is even more desirable in terms of lowering the OFF current value toform an offset region (a region which is formed from a semiconductorlayer having the same composition as the channel forming regions and towhich a gate voltage is not applied) between the channel forming regionsand the LDD regions. In the case of a multi-gate structure having two ormore gate electrodes, the high concentration region formed between thechannel forming regions is effective in lowering the OFF current value.

The OFF current value can be lowered sufficiently when the TFT havingthe multi-gate structure is used for the switching TFT 201 of the pixelas described above. In other words, that the OFF current value is smallmeans that a voltage applied to the gate of the current controlling TFTcan be held longer. This provides an advantage in that the gate voltageof the current controlling TFT can be held until the next writing periodeven when the capacitor (condenser) for holding the electric potential,as shown in FIG. 1 of Japanese Patent Application Laid-open No. Hei8-241048, is downsized or omitted.

Next, the current controlling TFT 202 that is a P-channel TFT is formedto have a source region 31, a drain region 32, an active layer includingan LDD region 33 and a channel forming region 34, a gate insulating film18, a gate electrode 35, a first interlayer insulating film 20, a sourcewiring 36, and a drain wiring 37. The gate electrode 35 has the singlegate structure, but may take a multi-gate structure.

As shown in FIG. 1, the drain region 14 of the switching TFT 201 isconnected to the gate electrode 35 of the current controlling TFT 202.To be specific, the gate electrode 35 of the current controlling TFT 202is electrically connected through the drain wiring 22 to the drainregion 14 of the switching TFT 201. The source wiring 36 is connected toa current supply line (also called power supply line) 212 (see FIG. 2A).

The current controlling TFT 202 is an element for controlling the amountof current flowing into an EL element 203. Considering degradation ofthe EL element, it is not desirable to cause a large current to flowthrough the EL element 203. Therefore, in order to prevent excessivecurrent flow in the current controlling TFT 202, a channel length (L) ispreferably designed to be rather long. Desirably, the channel length forone pixel is 0.5 to 2 μA (more desirably, 1 to 1.5 μA).

As shown in FIG. 6, the channel length of the switching TFT is given asL1 (L1=L1 a+L1 b) and the channel width thereof as W1, whereas thechannel length of the current controlling TFT is given as L2 and thechannel width thereof as W2. Then, based on the above, W1 is preferably0.1 to 5 μm (typically 0.5 to 2 μm), W2 is preferably 0.5 to 10 μm(typically 2 to 5 μm). L1 is preferably 0.2 to 18 μm (typically 2 to 15μm), and L2 is preferably 1 to 50 μm (typically 10 to 30 μm). However,the present invention is not limited to the values above.

The length (width) of the LDD region formed in the switching TFT 201 isappropriately set to 0.5 to 3.5 μm, typically 2.0 to 2.5 μm.

The EL display device shown in FIG. 1 is characterized in that the LDDregion 33 is formed between the drain region 32 and the channel formingregion 34 in the current controlling TFT 202, and that the LDD region 33overlaps with the gate electrode 35 through the gate insulating film 18sandwiched therebetween. The length of the LDD region overlapping withthe gate electrode is appropriately set to 0.1 to 3 μm (preferably 0.3to 1.5 μm).

The present invention is characterized by actively using, as a capacitor(condenser) for holding a voltage (for holding electric charges), theparasitic capacitor (gate capacitor) formed between the gate electrodeand the active layer that overlaps with the gate electrode through thegate insulating film sandwiched therebetween.

In this embodiment mode, the capacitance of the gate capacitor placedbetween the gate electrode 35 and the active layer (specifically, theLDD region 33) is increased by forming the LDD region 33 shown in FIG.1, and this gate capacitor is used as a capacitor (condenser) forholding a voltage applied to the gate of the current controlling TFT202. Another capacitor may be formed separately, of course, but byadopting the structure of this embodiment mode, the area for forming thecapacitor (condenser) can be omitted to thereby increase the effectivelight emission area of the pixel.

In particular, if the EL display device of the present invention isoperated on a digital driving system, a very small capacitor (condenser)is satisfiable as the capacitor (condenser) for holding the voltage. Thecapacitance thereof is, for example, about one fifth or one tenthcompared to the case of an analog driving system. Though it is difficultto present specific values in a wholesale manner because they varydepending upon the ability of the switching TFT and the currentcontrolling TFT, 5 to 30 fF (femto-farad) will be sufficient.

If the switching TFT takes a multi-gate structure to lower the OFFcurrent value as shown in FIG. 1, the capacitance required for thecapacitor (condenser) to hold the voltage is further reduced. Thereforeno problem is caused by the structure in which only the gate capacitoris used as the capacitor (condenser) for holding the voltage as shown inFIG. 1.

Although the current controlling TFT 202 has the single gate structurein this embodiment mode, it may take a multi-gate structure in which aplurality of TFTs are connected in series. Alternatively, it may be astructure capable of radiating heat with high efficiency, in which aplurality of TFTs are connected parallel to each other to substantiallydivide the channel forming region into plural sections. This is aneffective structure as a countermeasure against degradation by heat.

Reference symbol denotes a first passivation film with film thickness of10 nm to 1 μm (preferably 200 to 500 nm). An insulating film containingsilicon (a silicon oxide nitride film or a silicon nitride film isparticularly preferable) can be used as a material of the firstpassivation film. It is effective to impart heat releasing action to thefirst passivation film 38.

A second interlayer insulating film (planarizing film) 39 is formed onthe first passivation film 38 to level out a level difference caused bythe TFT. A preferred material for the second interlayer insulating film39 is an organic resin film, and a polyimide film, a polyamide film, anacrylic resin film, a BCB (benzocyclobuten) film, etc., are appropriate.Of course, an inorganic film may be used if it can satisfiably level outthe level difference.

It is very important to level out the level difference caused by the TFTusing the second interlayer insulating film 39. The EL layer to beformed later is so thin that the existence of a level difference maylead to inferior light emission. Therefore planarization beforeformation of a pixel electrode is required, so that the EL layer can beformed on a surface as flat as possible.

Denoted by reference symbol 40 is a pixel electrode formed from atransparent conductive film (anode of the EL element). The pixelelectrode is formed by opening a contact hole (aperture) piercingthrough the second interlayer insulating film 39 and the firstpassivation film 38, and then being brought into contact, in the thusformed aperture, with the drain wiring 37 of the current controlling TFT202. A conductive film mainly containing a compound of indium oxide andtin oxide or a compound of indium oxide and zinc oxide is preferablyused as the pixel electrode 40. The conductive film may of course belayered on another transparent conductive film to form a laminatestructure.

Next, an EL material is formed into a light-emitting layer 42. Althoughboth the inorganic EL material and the organic EL material may be usedas the EL material for the light-emitting layer, the organic EL materialthat is low in drive voltage is preferred. As the organic EL material,both the low molecular weight type (monomer type) organic EL materialand the high molecular weight type (polymer type) organic EL materialmay be used.

Representative monomer type organic EL material are Alq₃(8-hydroquinoline aluminum) and DSA (distyryl arylene derivative). Anyknown material other than these may also be used.

Polyparaphenylene vinylene (PPV), polyvinyl carbazole (PVK), etc., arenamed as an example of the polymer type organic EL material. Any knownmaterial may also be used, of course. Specifically, preferredarrangement is such that cyanopolyphenylene vinylene is used for alight-emitting layer that emits red light, polyphenylene vinylene for alight-emitting layer that emits green light, and polyphenylene vinyleneor polyalkylphenylene for a light-emitting layer that emits blue light.An appropriate film thickness thereof is 30 to 150 nm (preferably 40 to100 nm).

The light-emitting layer may be doped with a fluorescent substance(typically, coumarin 6, rubrene, Nile red, DCM, quinacridone, etc.) toshift the luminescence center to the fluorescent substance and obtainlight emission as desired. Any known fluorescent substance may be used.

If the monomer type organic EL material is used as the light-emittinglayer 42, the layer is formed by vacuum evaporation. On the other hand,spin coating, printing, the ink jet method, or dispensing is employed toform the light-emitting layer 42 from the polymer type organic ELmaterial. When forming the layer from the polymer type organic ELmaterial, however, the processing atmosphere is desirably a dry inertatmosphere that contains moisture in as small amount as possible. Inthis embodiment mode, the layer is formed from the polymer type organicEL material by spin coating.

The polymer type organic EL material is formed into the light-emittinglayer under normal pressure. However, the organic EL material is easilydegraded in the presence of moisture and oxygen. These degradationfactors therefore must be removed as much as possible from theprocessing atmosphere when forming the EL material into the layer.Preferred atmosphere is, for example, dry nitrogen atmosphere, dry argonatmosphere, and the like. Accordingly, it is desirable to place anapparatus for forming the light-emitting layer in a clean booth filledwith an inert gas and conduct the step of forming the light-emittinglayer in the inert atmosphere.

After thus forming the light-emitting layer 42, then an electroninjection layer 43 is formed. A monomer type organic material such aslithium fluoride or acetylacetonate complex is used for the electroninjection layer 43. A polymer type organic material or an inorganicmaterial may also be used, of course. An appropriate film thicknessthereof is 3 to 20 nm (preferably, 5 to 15 nm).

It should be noted that the materials mentioned above are merelyexemplary of organic materials usable as the light-emitting layer or theelectron injection layer of the present invention, and that there is noneed to limit the layer materials thereto. Also note that, though shownhere is a combination of the light-emitting layer and the electroninjection layer, the light-emitting layer may be combined with a holetransportation layer, a hole injection layer, an electron transportationlayer, a hole blocking layer, or an electron blocking layer.

Provided on the electron injection layer 43 is a cathode 44 formed froma conductive film having a small work function. As the conductive filmhaving a small work function, an aluminum alloy film, a copper alloyfilm, or a silver alloy film may be used. A laminate film consisting ofany of the alloy films mentioned above and another conductive film maybe used as well. The cathode 44 also serves as a passivation film forprotecting the organic EL material in the light-emitting layer and otherlayers from oxygen and moisture.

Upon formation of the cathode 44, the EL element 203 is completed. TheEL element 203 here is a capacitor (condenser) composed of the pixelelectrode (anode) 40, the light-emitting layer 42, the electroninjection layer 43, and the cathode 44. In this embodiment mode, thelight emitted from the light-emitting layer 42 is transmitted throughthe substrate 11 to be used, and hence a part of the pixel which is notoccupied by the TFT corresponds to the effective light-emission area.According to the present invention, the capacitor (condenser) forholding the gate voltage of the current controlling TFT 202 is takencare of by the current controlling TFT 202 with its own gate capacitor.The effective light emission area is thus wide, making it possible toprovide bright image display.

Though shown in this embodiment mode is the structure of a planar typeTFT as an example of using a top gate type TFT, a bottom gate type TFT(typically, an inverted stagger type TFT) may also be used.

[Embodiment 1 ]

The embodiments of the present invention are explained using FIGS. 3A to5C. A method of simultaneous manufacture of a pixel portion, and TFTs ofa driver circuit portion formed in the periphery of the pixel portion,is explained here. Note that in order to simplify the explanation, aCMOS circuit is shown as a basic circuit for the driver circuits.

First, as shown in FIG. 3A, a base film 301 is formed with a 300 nmthickness on a glass substrate 300. Silicon nitride oxide films arelaminated as the base film 302 in this embodiment. It is good to set thenitrogen concentration at between 10 and 25 wt % in the film contactingthe glass substrate 300. Further, it is advantageous to provide the basefilm with a heat radiation function, a DLC (diamond like carbon) filmcan also be provided.

Next, an amorphous silicon film (not shown in the figures) is formedwith a thickness of 50 nm on the base film 301 by a known depositionmethod. Note that it is not necessary to limit this to the amorphoussilicon film, and another film may be formed provided that it is asemiconductor film containing an amorphous structure (including amicrocrystalline semi conductor film). In addition, a compoundsemiconductor film containing an amorphous structure, such as anamorphous silicon germanium film, may also be used. Further, the filmthickness may be made from 20 to 100 nm.

The amorphous silicon film is then crystallized by a known method,forming a crystalline silicon film (also referred to as apolycrystalline silicon film or a polysilicon film) 302. Thermalcrystallization using an electric furnace, laser annealingcrystallization using a laser, and lamp annealing crystallization usingan infrared lamp exist as known crystallization methods. Crystallizationis performed in this embodiment using light from an excimer laser whichuses XeCl gas.

Note that pulse emission type excimer laser light formed into a linearshape is used in this embodiment, but a rectangular shape may also beused, and continuous emission argon laser light and continuous emissionexcimer laser light can also be used. Further, the first harmonic laserto the forth harmonic laser of YAG laser can also be used.

Next, as shown in FIG. 3B, a protecting film 303 is formed on thecrystalline silicon film 302 with a silicon oxide film having athickness of 130 nm. This thickness may be chosen within the range of100 to 200 nm (preferably between 130 and 170 nm). Furthermore, otherfilms may also be used providing that they are insulating filmscontaining silicon. The protecting film 303 is formed so that thecrystalline silicon film is not directly exposed to plasma duringaddition of an impurity, and so that it is possible to have delicateconcentration control of the impurity.

Resist masks 304 a and 304 b are then formed, and an impurity elementwhich imparts n-type conductivity (hereafter referred to as an n-typeimpurity element) is added via the protecting film 303. Note thatelements residing in periodic table group 15 are generally used as then-type impurity element, and typically phosphorus or arsenic can beused. Note that a plasma doping method is used, in which phosphine (PH₃)is plasma activated without separation of mass, and phosphorus is addedat a concentration of 1×1018 atoms/cm³ in this embodiment. An ionimplantation method, in which separation of mass is performed, may alsobe used, of course.

The dose amount is regulated so that the n-type impurity element iscontained in n-type impurity regions 305, thus formed by this process,at a concentration of 2×10¹⁶ to 5×10¹⁹ atoms/cm³ (typically between5×10¹⁷ and 5×10¹⁸ atoms/cm³).

Next, resist masks 306 a and 306 b are then formed, and an impurityelement which imparts p-type conductivity (hereafter referred to as ap-type impurity element) is added via the protecting film 303. Note thatelements residing in periodic table group 13 are generally used as thep-type impurity element, and typically, boron or gallium can be used.Note that a plasma doping method is used, in which diborane (B₂H₆) isplasma activated without separation of mass in this embodiment. An ionimplantation method, in which separation of mass is performed, may alsobe used, of course. (See FIG. 3C)

The dose amount is regulated so that the p-type impurity element iscontained in p-type impurity regions 307 and 308, thus formed by thisprocess, at a concentration of 1×10¹⁵ to 5×10¹⁷ atoms/cm³ (typicallybetween 1×10¹⁶ and 1×10¹⁷ atoms/cm³). The p-type impurity element isused to regulate the threshold voltage of n-channel type TFT.

Next, the protecting film 303 is removed, and an activation of the addedn-type impurity elements and p-type impurity elements is performed. Aknown technique of activation may be used as the means of activation,and activation is done in this embodiment by irradiation of excimerlaser light. A pulse emission type excimer laser and a continuousemission type excimer laser may both, of course, be used, and it is notnecessary to place any limits on the use of excimer laser light. Thepurpose is the activation of the added impurity element, and it ispreferable that irradiation is performed at an energy level at which thecrystalline silicon film does not melt. Note that the laser irradiationmay also be performed with the protecting film 303 in place.

The activation by heat treatment may also be performed along withactivation of the impurity element by laser light. When activation isperformed by heat treatment (furnace annealing), considering the heatresistance of the substrate, it is good to perform heat treatment on theorder of 450 to 550° C.

Unnecessary portions of the crystalline silicon film are removed next,as shown in FIG. 3D, and island shape semiconductor films (hereafterreferred to as active layers) 309 to 312 are formed.

Then, as shown in FIG. 3E, a gate insulating film 313 is formed,covering the active layers 309 to 312. An insulating film containingsilicon and with a thickness of 10 to 200 nm, preferably between 50 and150 nm, may be used as the gate insulating film 313. A single layerstructure or a lamination structure may be used. A 110 nm thick siliconnitride oxide film is used in this embodiment.

A conducting film with a thickness of 200 to 400 nm is formed next andpatterned, forming gate electrodes 314 to 318. Note that in thisembodiment, the gate electrodes and lead wirings electrically connectedto the gate electrodes (hereafter referred to as gate wirings) areformed from different materials. Specifically, a material having a lowerresistance than that of the gate electrodes is used for the gatewirings. This is because a material which is capable of beingmicro-processed is used as the gate electrodes, and even if the gatewirings cannot be micro-processed, the material used for the wirings haslow resistance. Of course, the gate electrodes and the gate wirings mayalso be formed from the same material.

Further, the gate wirings may be formed by a single layer conductingfilm, and when necessary, it is preferable to use a two layer or a threelayer lamination film. All known conducting films can be used as thegate electrode material. However, as stated above, it is preferable touse a material which is capable of being micro-processed, specifically,a material which is capable of being patterned to a line width of 2 μmor less.

Typically, it is possible to use a film made of an element selected fromtantalum (Ta), titanium (Ti), molybdenum (Mo), tungsten (W), chromium(Cr), and silicon (Si), a film of nitride of the above element(typically a tantalum nitride film, tungsten nitride film, or titaniumnitride film), an alloy film of combination of the above elements(typically Mo—W alloy, Mo—Ta alloy), or a silicide film of the aboveelement (typically a tungsten silicide film, titanium silicide film). Ofcourse, the films may be used as a single layer or a laminate layer.

In this embodiment, a laminate film of a tungsten nitride (WN) filmhaving a thickness of 30 nm and a tungsten (W) film having a thicknessof 370 nm is used. These may be formed by a sputtering method. When aninert gas of Xe, Ne or the like is added as a sputtering gas, filmpeeling due to stress can be prevented.

The gate electrodes 315 and 318 are formed at this time so as to overlapand sandwich a portion of the n-type impurity regions 305, a part ofp-type impurity region 308, and the gate insulating film 313respectively. This overlapping portion later becomes an LDD regionoverlapping the gate electrode.

Next, an n-type impurity element (phosphorus is used in this embodiment)is added in a self-aligning manner with the gate electrodes 314 to 318as masks, as shown in FIG. 4A. The addition is regulated so thatphosphorus is added to impurity regions 319 to 326 thus formed at aconcentration of {fraction (1/10)} to ½ that of the n-type impurityregions 305 (typically between ¼ and ⅓). Specifically, a concentrationof 1×10¹⁶ to 5×10¹⁸ atoms/cm³ (typically 3×10¹⁷ to 3×10¹⁸ atoms/cm³) ispreferable.

Resist masks 327 a to 327 d are formed next, with a shape covering thegate electrodes etc, as shown in FIG. 4B, and an n-type impurity element(phosphorus is used in this embodiment) is added, forming impurityregions 328 to 332 containing a high concentration of phosphorus. Iondoping using phosphine (PH₃) is also performed here, and is regulated sothat the phosphorus concentration of these regions is from 1×10²⁰ to1×10²¹ atoms/cm³ (typically between 2×10²⁰ and 5×10²⁰ atoms/cm³).

A source region or a drain region of the n-channel TFT is formed by thisprocess, and in the switching TFT, a portion of the n-type impurityregions 322 to 324 formed by the process of FIG. 4A remains. Theseremaining regions correspond to the LDD regions 15 a to 15 d of theswitching TFT in FIG. 1.

Next, as shown n FIG. 4C, the resist masks 327 a to 327 d are removed,and a new resist mask 333 is formed. A p-type impurity element (boron isused in this embodiment) is then added, forming impurity regions 334 to337 containing a high concentration of boron. Boron is added here at aconcentration of 3×10²⁰ to 3×10²¹ atoms/cm³ (typically between 5×10²⁰and 1×10²¹ atoms/cm³) by ion doping using diborane (B₂H₆).

Note that phosphorus has already been added to the impurity regions 334to 337 at a concentration of 1×10¹⁶ to 5×10¹⁸ atoms/cm³, but boron isadded here at a concentration of at least 3 times than of thephosphorus. Therefore, the n-type impurity regions already formedcompletely invert to p-type, and function as p-type impurity regions.

Next, after removing the resist mask 333, the n-type and p-type impurityelements added at various concentrations are activated. Furnaceannealing, laser annealing, or lamp annealing may be performed as ameans of activation. Heat treatment is performed in this embodiment in anitrogen atmosphere for 4 hours at 550° C. in an electric furnace.

It is important to remove as much of the oxygen in the atmosphere aspossible at this time. This is because if any oxygen exists, then theexposed surface of the electrode is oxidized, inviting an increase inresistance, and at the same time it becomes more difficult to later makean ohmic contact. It is therefore preferable that the concentration ofoxygen in the processing environment in the above activation processshould be 1 ppm or less, desirably 0.1 ppm or less.

After the activation process is completed, a gate wiring 338 with athickness of 300 nm is formed next. A metallic film having aluminum (Al)or copper (Cu) as its principal constituent (comprising 50 to 100% ofthe composition) may be used as the material of the gate wiring 338. Aswith the gate wiring 211 of FIGS. 2A and 2B, the gate wiring 338 isformed with a placement so that the gate electrodes 316 and 317 of theswitching TFTs (corresponding to gate electrodes 19 a and 19 b ofFIG. 1) are electrically connected. (See FIG. 4D.)

The wiring resistance of the gate wiring can be made extremely small byusing this type of structure, and therefore a pixel display region(pixel portion) having a large surface area can be formed. Namely, thepixel structure of this embodiment is extremely effective because an ELdisplay device having a screen size of a 10 inch diagonal or larger (inaddition, a 30 inch or larger diagonal) is realized due to thisstructure.

A first interlayer insulating film 339 is formed next, as shown in FIG.5A. A single layer insulating film containing silicon is used as thefirst interlayer insulating film 339, while a lamination film may becombined in between. Further, a film thickness of between 400 nm and 1.5μm may be used. A lamination structure of an 800 nm thick silicon oxidefilm on a 200 nm thick silicon nitride oxide film is used in thisembodiment.

In addition, heat treatment is performed for 1 to 12 hours at 300 to450° C. in an environment containing between 3 and 100% hydrogen,performing hydrogenation. This process is one of hydrogen termination ofdangling bonds in the semiconductor film by hydrogen which is thermallyactivated. Plasma hydrogenation (using hydrogen activated by a plasma)may also be performed as another means of hydrogenation.

Note that the hydrogenation step may also be inserted during theformation of the first interlayer insulating film 339. Namely, hydrogenprocessing may be performed as above after forming the 200 nm thicksilicon nitride oxide film, and then the remaining 800 nm thick siliconoxide film may be formed.

Next, a contact hole is formed in the first interlayer insulating film339, and source wiring lines 340 to 343 and drain wiring lines 344 to346 are formed. In this embodiment, this electrode is made of a laminatefilm of three-layer structure in which a titanium film having athickness of 100 nm, an aluminum film containing titanium and having athickness of 300 nm, and a titanium film having a thickness of 150 nmare continuously formed by a sputtering method. Of course, otherconductive films may be used.

A first passivation film 347 is formed next with a thickness of 50 to500 nm (typically between 200 and 300 nm). A 300 nm thick siliconnitride oxide film is used as the first passivation film 347 in thisembodiment. This may also be substituted by a silicon nitride film. Notethat it is effective to perform plasma processing using a gas containinghydrogen such as H₂ or NH₃ etc. before the formation of the siliconnitride oxide film. Hydrogen activated by this preprocess is supplied tothe first interlayer insulating film 339, and the film quality of thefirst passivation film 347 is improved by performing heat treatment. Atthe same time, the hydrogen added to the first interlayer insulatingfilm 339 diffuses to the lower side, and the active layers can behydrogenated effectively.

Next, as shown in FIG. 5B, a second interlayer insulating film 348 madeof organic resin is formed. As the organic resin, it is possible to usepolyimide, polyamide, acryl, BCB (benzocyclobutene) or the like.Especially, since the second interlayer insulating film 348 is primarilyused for flattening, acryl excellent in flattening properties ispreferable. In this embodiment, an acrylic film is formed to a thicknesssufficient to flatten a stepped portion formed by TFTs. It isappropriate that the thickness is preferably made 1 to 5 μm (morepreferably, 2 to 4 μm).

A contact hole reaching a drain wiring line 346 is formed through thesecond interlayer insulating film 348, and the first passivation film347, and a pixel electrode 349, which is made of transparent conductivefilm, is formed. In this embodiment, a conductive film having athickness of 120 nm is formed, which is made of combined element ofindium-tin oxide and zinc oxide, as a pixel electrode 349.

Next, an insulating film 350 is formed as shown in FIG. 5C. Theinsulating film 350 is formed by patterning the organic resin film orthe insulating film contains 100-300 nm silicon. This insulating film350 is formed to fill the space between pixels (pixel electrodes). Thisinsulating film 350 is formed for organic EL material, which is formednext, of luminescence layer not to overlap the edge portion of pixelelectrode 349.

A light emitting layer 351 is next formed by the spin coating method.Specifically, an organic EL material that becomes the light emittinglayer 351 is dissolved in a solvent such as chloroform, dichloromethane,xylene, toluene, and tetrahydrofuran, and is then applied. Thereafter,heat treatment is performed to volatilize the solvent. A film (lightemitting layer) made of the organic EL material is thus formed. In thisembodiment, a paraphenylene vinylene is used for the light emittinglayer emitting green color. The light emitting layer is formed to athickness of 50 nm. In addition, 1.2 dichloromethane is used as asolvent, and then volatilized by performing heat treatment on a hotplate at 80 to 150° C. for 1 minute.

Next, an electron injection layer 352 is formed to a thickness of 20 nm.As an electron injection layer 352, lithium fluoride is formed by theevaporation. As an electron injection layer 352, other polymer organicmaterial and monomer organic material can be used. The inorganicmaterial can also be used.

A two-layered structure made of the light emitting layer and theelectron injection layer is formed in Embodiment 1. However, otherlayers such as a hole transporting layer, a hole injection layer, and anelectron transporting layer may also be provided. Examples of variouslamination structures of such combination of layers have been reported,and any structure may be used for the present invention.

After the formation of the light emitting layer 351 and the electroninjection layer 352, an cathode 353 made of a small work functiontransparent conductive film is formed to a thickness of 350 nm. In thisembodiment, an alloy of lithium and aluminum is formed by vacuumevaporation method.

An active matrix substrate having a structure as shown in FIG. 5C isthus completed. Note that after the formation of the insulating film350, it is effective to use the multi-chamber method (or the in-linemethod) of the thin film deposition apparatus for the process of formingthe films until the formation of the cathode 353, in succession andwithout exposure to the atmosphere.

In the active matrix substrate of this embodiment, TFTs having optimalstructures are arranged not only in the pixel portion but also in thedriver circuit portion, thereby indicating an extremely high reliabilityand increasing its operation performance.

First, a TFT having a structure to decrease hot carrier injection so asnot to drop the operation speed thereof as much as possible is used asan n-channel TFT 205 of a CMOS circuit forming a driver circuit portion.Note that the driver circuit here includes a shift register, a buffer, alevel shifter, a sampling circuit (sample and hold circuit), a D/Aconverter and the like.

In the case of this embodiment, as shown in FIG. 5C, an active layer ofthe n-channel TFT 205 is composed of a source region 355, a drain region356, an LDD region 357, and a channel forming region 358. The LDD region357 overlaps the gate electrode 315 via the gate insulating film 313.

Consideration not to drop the operation speed is the reason why the LDDregion is formed at only the drain region side. In this n-channel TFT205, it is not necessary to pay attention to an OFF current value verymuch, rather, it is better to give importance to an operation speed.Thus, it is desirable that the LDD region 357 is made to completelyoverlap the gate electrode to decrease a resistance component to aminimum.

The p-channel TFT 206 in the CMOS circuit includes the source region334, the drain region 335 and the channel formation region 359.Furthermore, deterioration due to the injection of hot carriers isalmost negligible, and thus, it is not necessary to provide any LDDregion however it is also possible to provide it.

Note that, in practice, it is preferable to additionally performpackaging (sealing) after completing up through FIG. 5C by using ahighly airtight protective film which has very little gas leakage (suchas a laminate film or an ultraviolet cured resin film) or a sealingmaterial that is transmissive, so that there is no exposure to theatmosphere. By making the surrounded portion by the sealing material aninert environment, an inert liquid material and an inert solid materialand by placing a drying agent (for example, barium oxide) within thesealing material, the reliability of the EL element is increased.

Furthermore, aft the airtightness is increased by the packing processingetc., a connector (a flexible printed circuit, FPC) for connectingoutput terminals from elements or circuits formed on the substrate andexternal signal terminals, is attached, completing an electronic deviceusing EL element. The electronic device of this specification includes aconnector for input a signal from outside and integral circuit which isconnected to the connector.

Here, the structure of the EL display device of this embodiment will bedescribed with reference in FIG. 7. The EL display device of thisembodiment is constituted by a source side driver circuit 701, a pixelportion 708, and a gate side driver circuit 709. Further, in thisembodiment, the driver circuit portion is a general term including thesource side driver circuit and the gate side driver circuit.

In this embodiment, an n-channel TFT having multi-gate structure isprovided as a switching TFT in the pixel portion 708, the switching TFTis arranged to the intersection of gate wiring and source wiring whichare connected to the gate side driver circuit 709 and the source sidedriver circuit 701 respectively. Further, the drain region of theswitching TFT is connected to the gate electrode of p-channel typecurrent control TFT electrically.

The source side driver circuit 701 is provided with a shift register702, a buffer 703, a latch (A) 704, a buffer 705, a latch (B) 706 and abuffer 707. Further, in the case of analog driver, the sampling circuitis provided instead of a latch (A) and a latch (B). The gate side drivercircuit 709 is provided with a shift register 710, and a buffer 711.

Further, not shown in the figure, the gate side driver circuit can beprovided at the opposite side of the gate driver circuit 709 via thepixel portion 708. In this case, the both side own jointly gate wiringsin the same structure. The structure is if the one is destroyed, theother one send a gate signal to operate a pixel portion correctly.

The foregoing structure can be easily realized by manufacturing TFTs inaccordance with the manufacturing processes shown in FIGS. 3A to 5C. Inthis embodiment, although only the structure of the pixel portion andthe driver circuit portion is shown, if the manufacturing processes ofthis embodiment are used, it is possible to form a logical circuit, suchas a signal dividing circuit, a D/A converter circuit, an operationalamplifier circuit, a γ-correction circuit, on the same substrate, andfurther, it is considered that a memory portion, a microprocessor, orthe like can be formed.

Furthermore, an explanation of the EL display device of this embodiment,containing the sealing material to protect an EL element, is made usingFIGS. 8A and 8B. Note that, when necessary, the reference symbols usedin FIG. 7 is cited.

FIG. 8A is a diagram showing the top view of a state of complete sealingprocess to protect an EL element. Indicated by dotted lines, referencenumeral 708 denotes a pixel portion, 709 denotes a gate side drivercircuit, and 701 denotes a source side driver circuit. Reference numeral801 denotes a cover material, 802 denotes a first seal member, 803denotes a second seal member and a filling material (not shown in thefigure) is provided between an active matrix substrate and a portioncover material 801 which is enclosed by the first seal member 802.

Further, reference numeral 804 denotes a connection wiring to transmitthe signal which is input to the source side driver circuit 701 and thegate side driver circuit 709. The connection wiring accepts a videosignal and clock signal from an outside input terminal FPC 805.

Here, the cross-sectional view taken along line A-A′ of FIG. 8A is shownin FIG. 8B. It is to be noted that the same reference numerals are usedfor the same components in FIGS. 8A and 8B.

As shown in FIG. 8B, the pixel portion 708 and the gate side drivercircuit 709 are formed on the glass substrate 806. The pixel portion 708is formed of a plurality of pixels containing the current control TFT202 and the pixel electrode 349 which is electrically connected to thedrain region of the current control TFT 202. Further, the gate sidedriver circuit 709 is formed by using a CMOS circuit that is acomplementary combination of the n-channel TFT 205 and the p-channel TFT206.

The pixel electrode 349 functions as the anode of the EL element. Inaddition, the insulating film 350 is formed on both ends of the pixelelectrode 349, and the light emitting layer 351 and the electroninjection layer 352 are formed. The cathode 353 of the EL element isfurther formed on the top.

In the case of this embodiment, the cathode 353 also functions as acommon wiring to all the pixels, and is electrically connected to theFPC 805 through the connection wiring 804. Furthermore, all the elementscontained in the pixel portion 708 and the gate side driver circuit 709are covered by the cathode 353. The cathode 353 has a function as aconnection wiring but also a passivation film to protect an EL elementfrom water and oxygen, and as a electric field shielding film.

Next, after forming a first seal member 802 by a dispenser, scattering aspacer (not shown in figure) to attach a cover material 801. The spaceris scattered to maintain the distance between an active matrix substrateand cover material 801. And, the filling material 807 is filled insideof the first seal member 802 by a vacuum injecting method. Thetechnique, which is used in a cell assembling process of liquid crystaldisplay, can be used to foregoing process. It is preferable to use aphoto curing resin as the first seal member 802, but a thermally curableresin may also be used provided that the thermal resistance of the ELlayer permits. Note that it is preferable that the first seal member 802be a material through which as little moisture and oxygen as possibleare transmitted. Further, a drying agent may also be added to the insideof the first seal member 802.

Next, a filling material 807 is provided so as to cover the EL element.The filling material 807 also functions as an adhesive for attaching thecover material 801. As the filling material 807, polyimide, acryl, PVC(polyvinyl chloride), epoxy resins, silicone resins, PVB (polyvinylbutyral) or EVA (ethylene vinyl acetate) can be used.

It is preferable to place a drying agent (not shown in the figure)inside the filling material 807 because the absorbent effect can bemaintained. At this point, the drying agent may be an agent doped intothe filling material, or an agent enclosed in the filling material.Further, as above-mentioned spacer (not shown in the figure), it iseffective to use an absorbent material.

Further, in this embodiment, a glass plate, a quartz plate, a plasticplate, a ceramic plate, an FRP (Fiberglass-Reinforced Plastics) plate,PVF (polyvinyl fluoride) film, a Mylar film, a polyester film, or anacrylic film can be used as the cover material 801.

After using the filling material 807 to attach the cover material 801,the second seal member 803 is next formed so as to cover a side surface(the exposed surface) of the first seal member 802. The second sealmember 803 can use the same material as the first seal member 802.

The EL element is thus sealed into the filling material 807 by using theabove procedure, to thereby completely cut off the EL element from theexternal atmosphere and to prevent the penetration of substances such asmoisture and oxygen from the outside which stimulate the deteriorationof the EL element due to the oxidation of the EL layer. Accordingly,highly reliable EL display devices can be manufactured.

[Embodiment 2]

In this embodiment, an example of a case in which a pixel constitutionshown in FIG. 9 differs from that of the circuit diagram (constitution)shown in FIG. 2B. Note that in this embodiment, reference numeral 901denotes source wiring of a switching TFT 902, 903 denotes a gate wiringof a switching TFT 902, 904 denotes a current control TFT, 905 denotes acapacitor, 906 and 908 denote electric current supply lines, and 907denotes an EL element.

It is to be noted that the capacitor 905 employs a gate capacitance ofthe current control TFT 904. Substantially, the capacitor 905 is notprovided, and therefore it is indicated by a dotted line.

FIG. 9A is an example of a case in which the electric current supplyline 906 is common between two pixels. Namely, this is characterized inthat the two pixels are formed having linear symmetry around theelectric current supply line 906. In this case, the number of theelectric current supply line can be reduced, and therefore the pixelportion can be made with higher definition.

Further, FIG. 9B is an example of a case in which the electric currentsupply line 908 is formed parallel to the gate wiring 903. In FIG. 9B,the structure is formed such that the electric current supply line 908and the gate wiring 903 not to overlap. However, forming both indifferent layers, the films can be located overlapping each other withan insulating film therebetween. In this case, the exclusive surfacearea can be shared by the electric current supply line 908 and the gatewiring 903, and the pixel portion can be made with higher definition.

Furthermore, FIG. 9C is characterized in that the electric currentsupply line 908 and the gate wiring 903 a, 903 b are formed in parallel,similar to the structure of FIG. 9B, and additionally, in that the twopixels are formed so as to have linear symmetry around the electriccurrent supply line 908. In addition, it is effective to form theelectric current supply line 908 so as to overlap with one of the gatewirings 903 a, 903 b. In this case, the number of electric currentsupply lines can be reduced, and therefore the pixel portion can be madewith higher definition.

In addition, it is effective to employ the EL display device having thepixel structure of this embodiment as the display portion of theelectronic equipment of Embodiment 1.

[Embodiment 3]

In this embodiment, examples in which the element structure of theelectric current controlling TFT 202 shown in FIG. 1 is made a differentone, will be described with reference to FIGS. 10A to 10D. Specifically,examples in which the arrangement of the LDD region is made a differentone, will be described. Incidentally, the same portions as those of theelectric current controlling TFT 202 shown in FIG. 1 are designated bythe same symbols.

An electric current controlling TFT 202A shown in FIG. 10A is an examplein which the LDD region 33 is omitted from the electric currentcontrolling TFT 202 shown in FIG. 1. In the case shown in FIG. 1, sincethe switching TFT 201 has a triple-gate structure, an off current valueis very small, and if a digital driving system is used, the capacitanceof a capacitor for holding the electric potential of the gate of theelectric current controlling TFT 202A may be very small.

Thus, as shown in FIG. 10A of this embodiment, it is possible to holdthe electric potential of the gate of the electric current controllingTFT 202A only by a gate capacitance formed between a gate electrode 35and a drain region 32.

Next, an electric current controlling TFT 202B shown in FIG. 10B is anexample in which a gate electrode 35 overlaps with a part of an LDDregion 51 through a gate insulating film. In this case, a portion of theLDD region 51 not overlapping with the gate electrode 35 functions as aresistor so that it has an effect of decreasing the off current value.That is, by making the structure of FIG. 10B, it is possible to realizelowering of the off electric current value.

Next, an electric current controlling TFT 202C shown in FIG. 10C is anexample in which the LDD region 51 shown in FIG. 10B is provided at notonly the side of the source region 31 but also at the side of the drainregion 32. In this embodiment, an additional region is made an LDDregion 52. Such a structure is an effective structure in the case wherethe direction of flow of electrons is changed (source region and drainregion are inverted) like a sampling circuit used in an analog drivingsystem.

Thus, it is also possible to use the structure of FIG. 10C for aswitching TFT. Also in that case, it is possible to realize both thesuppression of deterioration due to the hot carrier injection and thelowering of the off current value at the same time.

Next, an electric current controlling TFT 202D shown in FIG. 10D is anexample in which the LDD region 33 shown in FIG. 1 is provided at boththe side of the source region 31 and the side of the drain region 32. Inthis embodiment, an additional region is made an LDD region 53. Such astructure is an effective structure in the case where the direction offlow of electrons is changed like a sampling circuit used in an analogdriving system.

Incidentally, any of the structures of this embodiment can besubstituted for the electric current controlling TFT 202 of theembodiment 1, and can also be combined with the embodiment 2.

[Embodiment 4]

In this embodiment, a description will be made on a case where aplurality of EL display devices of the present invention are fabricatedby using a large substrate (large wafer). Top views of FIGS. 11A to 13Bare used for the description. Incidentally, sectional views taken alongline A-A′ and B-B′ are also shown in the respective top views.

FIG. 11A is a view showing a state where a seal member is formed on anactive matrix substrate fabricated in the embodiment 1. Referencenumeral 61 designates the active matrix substrate, and first sealmembers 62 are provided at plural places. The first seal member 62 isformed while an opening portion 63 is secured.

A filler (rod-like spacer) may be added in the first seal member 62.Besides, spherical spacers 64 are sprinkled on the whole active matrixsubstrate 61. The spacers 64 may be sprinkled before or after formationof the first seal member 62. In either case, it is possible to securethe distance between the active matrix substrate 61 and a cover memberover the active matrix substrate 61 by the filler (not shown) or thespacers 64.

Incidentally, in view of suppression of deterioration of the EL element,it is effective to make the spacer 64 have a hygroscopic property.Besides, it is desirable that the spacer 64 is made of a materialtransmitting light emitted from the light emitting layer.

A pixel portion and a driving circuit portion are included in a region65 surrounded by the seal member 62. In this specification, a portionconstituted by the pixel portion and the driving circuit portion iscalled an active matrix portion. That is, the active matrix substrate 61is formed such that a plurality of active matrix portions each beingmade of a combination of the pixel portion and the driving circuitportion are formed on one large substrate.

FIG. 11B shows a state where a cover member 66 is bonded to the activematrix substrate 61. In this specification, a cell including the activematrix substrate 61, the first seal member 62, and the cover member 66is called an active matrix cell.

A process similar to a cell assembling step of liquid crystal may beused for the above bonding. Besides, as the cover member 66, atransparent substrate (or transparent film) having the same area as theactive matrix substrate 61 may be used. Thus, in the state of FIG. 11B,it is used as the cover member common to all the active matrix portions.

After the cover member 66 is bonded, the active matrix cell is dividedinto parts. In this embodiment, when the active matrix substrate 61 andthe cover member 66 are divided into parts, a scriber is used. Thescriber is such a device that after a thin groove (scribe groove) isformed in the substrate, shock is given to the scribe groove to generatea crack along the scribe groove so that the substrate is divided intoparts.

Incidentally, as a device for dividing a substrate into parts, a diceris also known. The dicer is such a device that a hard cutter (alsoreferred to as dicing saw) is rotated at high speed and is put to asubstrate to divide it into parts. However, when the dicer is used,water is jetted to the dicing saw to prevent heat generation and splashof abrasive powder. Thus, in the case where the EL display device isfabricated, it is desirable to use the scriber, which does not usewater.

As the sequence forming the scribe groove in the active matrix substrate61 and the cover member 66, first, a scribe groove 67 a is formed in thedirection of the arrow (a), and next, a scribe groove 67 b is formed inthe direction of the arrow (b). At this time, the scribe groove passingthrough the vicinity of the opening portion 63 is formed to cut thefirst seal member 62. By doing so, since the opening portion 63 appearsat the end face of the active matrix cell, a subsequent injection stepof a filler is facilitated.

When the scribe grooves are formed in this way, a shock is given to thescribe grooves by an elastic bar of silicone resin or the like togenerate cracks, so that the active matrix substrate 61 and the covermember 66 are divided into parts.

FIG. 12A shows the state after the first division, and active matrixcells 68 and 69 each including two active matrix portions are formedthrough the division. Next, a filler 70 is injected into a space formedof the active matrix substrate 61, the first seal member 62 and thecover member 66 by a vacuum injection method. Since the vacuum injectionmethod is well known as a technique of injecting liquid crystal, itsexplanation is omitted. At this time, it is preferable that theviscosity of the filler 70 is 3 to 15 cp. The filler having suchviscosity may be selected, or desired viscosity may be made by dilutionwith a solvent or the like. Besides, the vacuum injection method may becarried out in the state where a drying agent is added in the filler.

In this way, the filler 70 is filled as shown in FIG. 12A. Incidentally,although this embodiment shows a system in which the filler 70 is filledinto the plurality of active matrix cells at the same time, the systemlike this is suitable for fabrication of a small EL display device witha diagonal of about 0.5 to 1 inch. On the other hand, when a large ELdisplay device with a diagonal of about 5 to 30 inches is fabricated, itis appropriate that after division into the respective active matrixcells is made, the filler 70 is filled.

After the filler 70 is filled in the manner described above, the filler70 is hardened so that the adhesiveness between the active matrixsubstrate 61 and the cover member 66 is further raised. When the filler70 is an ultraviolet ray curing resin, ultraviolet rays are irradiated,and when it is a thermosetting resin, heating is made. However, in thecase where the thermosetting resin is used, attention must be paid tothe heat resistance of the organic EL material.

Next, scribe grooves are again formed in the active matrix substrate 61and the cover member 66. As the sequence, first, a scribe groove 71 a isformed in the direction of the arrow (a), and next, a scribe groove 71 bis formed in the direction of the arrow (b). At this time, the scribegrooves are formed so that the area of the cover member 66 becomessmaller as compared with the active matrix substrate 61 after thedivision.

After the scribe grooves are formed in this way, a shock is given to thescribe grooves by an elastic bar of silicone resin or the like togenerate cracks, so that division into active matrix cells 72 to 75 ismade. FIG. 13A shows the state after the second division. Further, anFPC 76 is attached to each of the active matrix cells 72 to 75.

Finally, as shown in FIG. 13B, a second seal member 77 is formed so asto cover the substrate end face (exposed face of the first seal member62 or the filler 70) of each of the active matrix cells 72 to 75 and theFPC 76. The second seal member 77 may be formed of an ultraviolet raycuring resin or the like in which degassing hardly occurs.

By the process described above, the EL display device as shown in FIG.13B is completed. As described above, by carrying out this embodiment, aplurality of EL display devices can be fabricated from one substrate.For example, from a substrate of 620 mm×720 mm, six EL display deviceseach having a diagonal of 13 to 14 inches can be formed, or four ELdisplay devices each having a diagonal of 15 to 17 inches can be formed.Thus, a throughput can be greatly improved and manufacturing costs canbe reduced.

Incidentally, the fabricating process of an EL display device of thisembodiment can be used for fabrication of an EL display device includingany structure of the embodiments 1 to 3.

[Embodiment 5]

In this embodiment, a description will be made on an example of a casewhere the filler 70 is not used in the embodiment 4. This embodiment ischaracterized in that after an active matrix cell is placed in a vacuum,a dry inert gas pressurized to 1 to 2 atmospheres is sealed in a regionsurrounded by the first seal member 62. As the inert gas, nitrogen orrare gas (typically argon, helium or neon) may be used.

Incidentally, this embodiment can use the process of the embodiment 4 asit is, except that a material vacuum injected in the embodiment 4 ismade a gas. Thus, the fabricating process of the EL display device ofthis embodiment can be used for fabrication of the EL display deviceincluding any structure of the embodiments 1 to 3.

[Embodiment 6]

In the embodiments 1 to 5, although the description has been made on theEL display device, the present invention can also be used for an activematrix electrochromic display (ECD), field emission display (FED), orliquid crystal display (LCD).

That is, the present invention can be used for any electronic devices inwhich a self light-emitting device or a light receiving element iselectrically connected to an TFT.

[Embodiment 7]

In Embodiment 1 laser crystallization is used for formation method ofcrystal silicon film 302, in this embodiment in the case of usinganother crystallization method is described.

After forming an amorphous silicon film in this embodiment,crystallization can be performed using the technique recorded inJapanese Patent Application Laid-open No. Hei 7-130652 or JapanesePatent Application Laid-open No. Hei 8-78329. The technique recorded inthe above patent applications is one of obtaining a crystalline siliconfilm having good crystallinity by using an element such as nickel as acatalyst for promoting crystallization.

Further, after th crystallization process is completed process ofremoving the catalyst used in the crystallization may be performed. Inthis case, the catalyst may be gettered using the technique recorded inJapanese Patent Application Laid-open No. Hei 10-270363 or JapanesePatent Application Laid-open No. Hei 8-330602.

In addition, a TFT may be formed using the technique recorded in thespecification of Japanese Patent Application Serial No. Hei 11-076967 bythe applicant of the present invention.

Note that it is possible to freely combine the constitution of thepresent embodiment with the constitution of any of embodiments 1 to 6 ina case that an electronic device is produced.

[Embodiment 8]

In this embodiment, FIGS. 16A and 16B indicate image photographs of anEL display device which is fabricated by the present invention. FIG. 16Ais an image photograph of an EL display device when a monomer typeorganic EL material is used as the light-emitting layer. Further, FIG.16B is an image photograph of an EL display device produced when apolymer type organic EL material is used as the light-emitting layer.

[Embodiment 9]

The EL display device fabricated in accordance with the presentinvention is of the self-emission type, and thus exhibits more excellentrecognizability of the displayed image in a light place as compared tothe liquid crystal display device. Furthermore, the EL display devicehas a wider viewing angle. Accordingly, the EL display device can beapplied to a display portion in various electric apparatuses. Forexample, in order to view a TV program or the like on a large-sizedscreen, the EL display device in accordance with the present inventioncan be used as a display portion of an EL display (i.e., a display inwhich an EL display device is installed into a frame) having a diagonalsize of 30 inches or larger (typically 40 inches or larger.)

The EL display includes all kinds of displays to be used for displayinginformation, such as a display for a personal computer, a display forreceiving a TV broadcasting program, a display for advertisementdisplay. Moreover, the EL display device in accordance with the presentinvention can be used as a display portion of other various electricapparatuses.

Such electric apparatuses include a video camera, a digital camera, agoggles-type display (head mount display), a car navigation system, asound reproduction device (an audio equipment), note-size personalcomputer, a game machine, a portable information terminal (a mobilecomputer, a portable telephone, a portable game machine, an electronicbook, or the like), an image reproduction apparatus including arecording medium (more specifically, an apparatus which can reproduce arecording medium such as a digital video disc (DVD), and includes adisplay for displaying the reproduced image), or the like. Inparticular, in the case of the portable information terminal, use of theEL display device is preferable, since the portable information terminalthat is likely to be viewed from a tilted direction is often required tohave a wide viewing angle. FIGS. 14A through 15B respectively showvarious specific examples of such electronic devices.

FIG. 14A illustrates an EL display which includes a frame 2001, asupport table 2002, a display portion 2003, or the like. The presentinvention is applicable to the display portion 2003. The EL display isof the self-emission type and therefore requires no back light. Thus,the display portion thereof can have a thickness thinner than that ofthe liquid crystal display device.

FIG. 14B illustrates a video camera which includes a main body 2101, adisplay portion 2102, an audio input portion 2103, operation switches2104, a battery 2105, an image receiving portion 2106, or the like. TheEL display device in accordance with the present invention can be usedas the display portion 2102.

FIG. 14C illustrates a portion (the right-half piece) of an EL displayof head mount type, which includes a main body 2201, signal cables 2202,a head mount band 2203, a display portion 2204, an optical system 2205,an EL display device 2206, or the like. The present invention isapplicable to the EL display device 2206.

FIG. 14D illustrates an image reproduction apparatus including arecording medium (more specifically, a DVD reproduction apparatus),which includes a main body 2301, a recording medium (a DVD or the like)2302, operation switches 2303, a display portion (a) 2304, anotherdisplay portion (b) 2305, or the like. The display portion (a) is usedmainly for displaying image information, while the display portion (b)is used mainly for displaying character information. The EL displaydevice in accordance with the present invention can be used as thesedisplay portions (a) and (b). The image reproduction apparatus includinga recording medium further includes a CD reproduction apparatus, a gamemachine or the like.

FIG. 14E illustrates a portable (mobile) computer which includes a mainbody 2401, a camera portion 2402, an image receiving portion 2403,operation switches 2404, a display portion 2405, or the like. The ELdisplay device in accordance with the present invention can be used asthe display portion 2405.

FIG. 14F illustrates a personal computer which includes a main body2501, a frame 2502, a display portion 2503, a key board 2504, or thelike. The EL display device in accordance with the present invention canbe used as the display portion 2503.

When the brighter luminance of light emitted from the EL materialbecomes available in the future, the EL display device in accordancewith the present invention will be applicable to a front-type orrear-type projector in which light including output image information isenlarged by means of lenses or the like to be projected.

The aforementioned electronic devices are more likely to be used fordisplay information distributed through a telecommunication path such asInternet, a CATV (cable television system), and in particular likely todisplay moving picture information. The EL display device is suitablefor displaying moving pictures since the EL material can exhibit highresponse speed. However, if the contour between the pixels becomesunclear, the moving pictures as a whole cannot be clearly displayed.Since the EL display device in accordance with the present invention canmake the contour between the pixels clear, it is significantlyadvantageous to apply the EL display device of the present invention toa display portion of the electronic devices.

A portion of the EL display device that is emitting light consumespower, so it is desirable to display information in such a manner thatthe light emitting portion therein becomes as small as possible.Accordingly, when the EL display device is applied to a display portionwhich mainly displays character information, e.g., a display portion ofa portable information terminal, and more particular, a portabletelephone or a sound reproduction equipment, it is desirable to drivethe EL display device so that the character information is formed by alight-emitting portion while a non-emission portion corresponds to thebackground.

With now reference to FIG. 15A, a cellular telephone is illustrated,which includes a main body 2601, an audio output portion 2602, an audioinput portion 2603, a display portion 2604, operation switches 2605, andan antenna 2606. The EL display device in accordance with the presentinvention can be used as the display portion 2604. The display portion2604 can reduce power consumption of the portable telephone bydisplaying white-colored characters on a black-colored background.

FIG. 15B illustrates a sound reproduction device, a car audio equipmentin concrete term, which includes a main body 2701, a display portion2702, and operation switches 2703 and 2704. The EL display device inaccordance with the present invention can be used as the display portion2702. Although the car audio equipment of the mount type is shown in thepresent embodiment, the present invention is also applicable to an audioof the set type. The display portion 2702 can reduce power consumptionby displaying white-colored characters on a black-colored background,which is particularly advantageous for the audio of the portable type.

As set forth above, the present invention can be applied variously to awide range of electric apparatuses in all fields. The electronic devicein the present embodiment can be obtained by utilizing an EL displaydevice having the configuration in which the structures in Embodiments 1through 8 are freely combined

According to the invention, it can be possible to omit the capacitorwhich is conventionally used to hold the gate voltage of the currentcontrol TFT, so that the effective light emission area per one pixel isgreatly increased. Thus, an electronic device of bright image displaycan be obtained. Furthermore, an electric apparatus with highperformance is provided by using the electronic device as its displayportion.

What is claimed is:
 1. An electronic device comprising: a first thinfilm transistor; a second thin film transistor having: a gate electrode,a gate insulating film, at least an LDD region, wherein the gateelectrode of the second thin film transistor is electrically connectedto a drain wiring of the first thin film transistor; a self lightemitting element, wherein the self light emitting element iselectrically connected to a drain wiring of the second thin filmtransistor, wherein the second thin film transistor is a p-channel thinfilm transistor, wherein at least a portion of the LDD region of thesecond thin film transistor is overlapped with the gate electrode withthe gate insulating film interposed therebetween.
 2. A device accordingto claim 1, wherein the LDD region of the second thin film transistorincludes a p-type impurity element at a concentration in a range of1×10¹⁵ to 5×10¹⁷ atoms/cm³.
 3. An electric apparatus using theelectronic device of claim
 1. 4. An electronic device comprising: afirst thin film transistor; a second thin film transistor having: a gateelectrode, a gate insulating film, at least an LDD region, wherein thegate electrode of the second thin film transistor is electricallyconnected to a drain wiring of the first thin film transistor; a selflight emitting element, wherein the self light emitting element iselectrically connected to a drain wiring of the second thin filmtransistor, wherein the second thin film transistor is a p-channel thinfilm transistor, wherein at least a portion of the LDD region of thesecond thin film transistor is overlapped with the gate electrode withthe gate insulating film interposed therebetween, wherein the first thinfilm transistor includes a plurality of thin film transistors beingconnected in series.
 5. A device according to claim 4, wherein the LDDregion of the second thin film transistor includes a p-type impurityelement at a concentration in a range of 1×10¹⁵ to 5×10¹⁷ atoms/cm³. 6.An electric apparatus using the electronic device of claim
 4. 7. Anelectronic device comprising a pixel portion and a driver circuitportion, said electronic device comprising: an n-channel thin filmtransistor being formed in the driver circuit portion, said n-channelthin film transistor having: a first gate electrode, a first gateinsulating film, at least a first LDD region, wherein the first LDDregion is overlapped with the first gate electrode with the first gateinsulating film interposed therebetween, a first thin film transistorbeing formed in the pixel portion; a second thin film transistor beingformed in the pixel portion, said second thin film transistor having: asecond gate electrode, a second gate insulating film, at least a secondLDD region, a self light emitting element being formed in the pixelportion, wherein the self light emitting element is electricallyconnected to the second thin film transistor, wherein the second thinfilm transistor is a p-channel thin film transistor, wherein at least aportion of the second LDD region of the second thin film transistor isoverlapped with the second gate electrode with the second gateinsulating film interposed therebetween.
 8. A device according to claim7, wherein the second LDD region of the second thin film transistorincludes a p-type impurity element at a concentration in a range of1×10¹⁵ to 5×10¹⁷ atoms/cm³.
 9. An electric apparatus using theelectronic device of claim
 7. 10. An electronic device comprising apixel portion and a driver circuit portion, said electronic devicecomprising: an n-channel thin film transistor being formed in the drivercircuit portion, said n-channel thin film transistor having: a firstgate electrode, a first gate insulating film, at least a first LDDregion, wherein the first LDD region is overlapped with the first gateelectrode with the first gate insulating film interposed therebetween, afirst thin film transistor being formed in the pixel portion; a secondthin film transistor being formed in the pixel portion, said second thinfilm transistor having: a second gate electrode, a second gateinsulating film, at least a second LDD region, a self light emittingelement being formed in the pixel portion, wherein the self lightemitting element is electrically connected to the second thin filmtransistor, wherein the second thin film transistor is a p-channel thinfilm transistor, wherein at least a portion of the second LDD region ofthe second thin film transistor is overlapped with the second gateelectrode with the second gate insulating film interposed therebetween,wherein the thin film transistor includes a plurality of thin filmtransistors being connected in series.
 11. A device according to claim10, wherein the second LDD region of the second thin film transistorincludes a p-type impurity element at a concentration in a range of1×10¹⁵ to 5×10¹⁷ atoms/cm³.
 12. An electric apparatus using theelectronic device of claim 10.